The relevance of racial and ethnic identities for biomedical research and patient care increasingly is at issue, particularly in the emerging contexts of post-genomic research and genetic medicine. The relationship between biological relatedness and social construction of identity is not a direct one. Mistaken uses of social identity as a proxy for biological relatedness can harm entire categories of people by implying that they are biologically different from others. At the same time, though, some socially defined populations do have higher incidences of some diseases and higher frequencies of some polymorphisms and haplotypes, suggesting that there is some value in using social identity as an indicator for participant recruitment in research studies as well as for clinical diagnoses. One way of resolving the imperfect fit between biological relatedness and social identity, at least in the case of genetic research and medicine, is to develop approaches for rigorously specifying social identity (i.e., by constructing extended pedigrees with health history information that go beyond the family health history information typically collected in clinical situations). Thus, we will conduct an empirical study of two questions: 1) Does a rigorous investigation of study participants' social identities (i.e.. families, extended pedigrees, and racial and ethnic groups and subgroups) add scientific and clinical value compared with the standard use of self-reported family health histories and racial and ethnic identifies? 2) How do existing familial, group and subgroup social dynamics affect study participants' perceptions and concerns about the collection and use of third-party information for clinical and research purposes? We will adapt an approach we developed for historically stable Native North American populations to rigorously specify social identity in historically mobile, geographically dispersed African-American and Euro-American populations. Doing so will allow us to construct extended pedigrees and population subgroups that we will then use to investigate the scientific and clinical value of more rigorously specified social identities compared with currently standard practices. Finally, we will examine the implications of third-party information from the perspectives of study participants. We will conduct this project in the contexts of actual clinical populations.